It is well known that an athlete’s body composition can influence their athletic success. Previous studies have shown that fat-free mass (FFM) is related to strength, power, speed, and sport performance. However, fat-free mass may not be the most valid indicator of an athlete’s sport-related capabilities; most sports require locomotion or propulsion of the athlete’s body, which is affected by both the capacity to produce force and the overall size of the body. In addition, taller people naturally have more FFM due to their height. Fat-free mass index (FFMI) scales an individual’s FFM to their height, which removes the bias of height and may be a more valid characterization of muscularity that translates more directly to sport-related tasks.

In sports such as American football, training and nutrition practices are often geared towards increasing FFM. Researchers have previously suggested that 25 kg∙m-2 is the natural FFMI limit for resistance-trained males; this is important because identifying upper limits would enhance the ability to set realistic body composition goals for athletes. However, the research identifying this limit used a sample of lean individuals who were not competitive athletes. As such, it is possible that this “limit” has been underestimated. Collegiate football players are an ideal population for evaluating high FFMI values, based on the sport’s emphasis on strength, power, and body size. Furthermore, evaluating a large sample of collegiate football players allowed us to determine if FFMI differs between position groups or levels of competition. This information would be tremendously valuable to nutrition and strength & conditioning professionals who assist football players in identifying and reaching body composition goals that are suitable for their playing position.

What did you do and what did you find in this study?

For this study, we performed dual-energy x-ray absorptiometry (DEXA) scans on three separate college football teams, including two division I teams and one division II team. We compared FFMI values between position groups and levels of play, and results indicated that FFMI was significantly higher in division I players compared to division II. Further, FFMI was drastically different between position groups, with the highest values observed in offensive and defensive linemen, and the lowest values observed in offensive and defensive backs. We provided FFMI ranges for each specific position based on the data from division I athletes, which should assist players in setting position-specific goals for body composition. Most importantly, we found that 62 athletes had FFMI values above 25 kg∙m-2 (26.4% of the sample). This percentage was even higher when specifically looking at division I athletes (31.3%). The 97.5th percentile was 28.1 kg∙m-2, and the highest observed value was 31.7 kg∙m-2.

How do these findings impact the public?

Our results indicate that drug-tested, resistance-trained males can achieve FFMI values well beyond 25 kg∙m-2. We also determined that FFMI effectively discriminates between playing levels and playing positions. Coaches and athletes can use this information to set more realistic body composition goals, and college and professional football teams may use this position-specific data to assist with their recruiting and personnel decisions.